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                <h1 id="PHP字符串变量"><a href="#PHP字符串变量" class="headerlink" title="PHP字符串变量"></a>PHP字符串变量</h1><p>字符串变量用于存储并处理文本</p>
<h2 id="PHP中的字符串变量"><a href="#PHP中的字符串变量" class="headerlink" title="PHP中的字符串变量"></a>PHP中的字符串变量</h2><p>字符串变量用于包含有字符的值</p>
<p>在创建字符串以后，我们就可以对他进行操作。可以直接在函数中使用字符串，或者把它存储在变量中。在下面的实例中，我们创建一个名为 txt 的字符串变量，并赋值为 “Hello world!” 。然后我们输出 txt 变量的值</p>
<pre class=" language-php+HTML"><code class="language-php+HTML"><?php
$txt = "hello world";
echo $txt;
?></code></pre>
<ul>
<li>赋予一个文本值给变量时，请记得给文本值加上单引号或着双引号</li>
</ul>
<h2 id="PHP并置运算符"><a href="#PHP并置运算符" class="headerlink" title="PHP并置运算符"></a>PHP并置运算符</h2><p>在PHP中，只有一个字符串运算符</p>
<p>并置运算符(.)用于把两个字符串值连接起来</p>
<pre class=" language-php"><code class="language-php"><span class="token delimiter">&lt;?php</span>
<span class="token variable">$txt_1</span> <span class="token operator">=</span> <span class="token string">"dxyd"</span>
<span class="token variable">$txt_2</span> <span class="token operator">=</span> <span class="token string">"hello world"</span>
<span class="token keyword">echo</span> <span class="token variable">$txt_1</span><span class="token punctuation">.</span><span class="token string">" "</span><span class="token punctuation">.</span><span class="token variable">$txt_2</span>
<span class="token delimiter">?></span></code></pre>
<h2 id="PHP-strlen-函数"><a href="#PHP-strlen-函数" class="headerlink" title="PHP strlen()函数"></a>PHP strlen()函数</h2><p>strlen() 函数返回字符串的长度（字节数）</p>
<h2 id="PHP-strpos-函数"><a href="#PHP-strpos-函数" class="headerlink" title="PHP strpos()函数"></a>PHP strpos()函数</h2><p>strpos() 函数用于在字符串内查找一个字符或一段指定的文本</p>
<p>如果在字符串中找到匹配，该函数会返回第一个匹配的字符位置。如果未找到匹配，则返回 FALSE</p>
<pre class=" language-php"><code class="language-php"><span class="token delimiter">&lt;?php</span>
<span class="token keyword">echo</span> <span class="token function">strpos</span><span class="token punctuation">(</span><span class="token string">"hello dxyd"</span><span class="token punctuation">,</span><span class="token string">"dxyd"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token delimiter">?></span>             <span class="token shell-comment comment">#将输出：6 </span></code></pre>
<h1 id="PHP运算符"><a href="#PHP运算符" class="headerlink" title="PHP运算符"></a>PHP运算符</h1><table>
<thead>
<tr>
<th>运算符</th>
<th align="left">描述</th>
</tr>
</thead>
<tbody><tr>
<td>-x</td>
<td align="left">x取反</td>
</tr>
<tr>
<td>a.b</td>
<td align="left">连接两个字符串</td>
</tr>
</tbody></table>
<hr>
<p>a.=b        ==        a=a.b</p>
<h2 id="PHP逻辑运算符"><a href="#PHP逻辑运算符" class="headerlink" title="PHP逻辑运算符"></a>PHP逻辑运算符</h2><table>
<thead>
<tr>
<th align="left">运算符</th>
<th align="left">名称</th>
<th align="left">描述</th>
<th align="left">实例</th>
</tr>
</thead>
<tbody><tr>
<td align="left">x and y</td>
<td align="left">与</td>
<td align="left">如果 x 和 y 都为 true，则返回 true</td>
<td align="left">x=6 y=3 (x &lt; 10 and y &gt; 1) 返回 true</td>
</tr>
<tr>
<td align="left">x or y</td>
<td align="left">或</td>
<td align="left">如果 x 和 y 至少有一个为 true，则返回 true</td>
<td align="left">x=6 y=3 (x= =6 or y==5) 返回 true</td>
</tr>
<tr>
<td align="left">x xor y</td>
<td align="left">异或</td>
<td align="left">如果 x 和 y 有且仅有一个为 true，则返回 true</td>
<td align="left">x=6 y=3 (x= =6 xor y==3) 返回 false</td>
</tr>
<tr>
<td align="left">x &amp;&amp; y</td>
<td align="left">与</td>
<td align="left">如果 x 和 y 都为 true，则返回 true</td>
<td align="left">x=6 y=3 (x &lt; 10 &amp;&amp; y &gt; 1) 返回 true</td>
</tr>
<tr>
<td align="left">x || y</td>
<td align="left">或</td>
<td align="left">如果 x 和 y 至少有一个为 true，则返回 true</td>
<td align="left">x=6 y=3 (x= =5 || y==5) 返回 false</td>
</tr>
<tr>
<td align="left">! x</td>
<td align="left">非</td>
<td align="left">如果 x 不为 true，则返回 true</td>
<td align="left">x=6 y=3 !(x==y) 返回 true</td>
</tr>
</tbody></table>
<h2 id="PHP-数组运算符"><a href="#PHP-数组运算符" class="headerlink" title="PHP 数组运算符"></a>PHP 数组运算符</h2><table>
<thead>
<tr>
<th align="left">运算符</th>
<th align="left">名称</th>
<th align="left">描述</th>
</tr>
</thead>
<tbody><tr>
<td align="left">x + y</td>
<td align="left">集合</td>
<td align="left">x 和 y 的集合</td>
</tr>
<tr>
<td align="left">x == y</td>
<td align="left">相等</td>
<td align="left">如果 x 和 y 具有相同的键/值对，则返回 true</td>
</tr>
<tr>
<td align="left">x === y</td>
<td align="left">恒等</td>
<td align="left">如果 x 和 y 具有相同的键/值对，且顺序相同类型相同，则返回 true</td>
</tr>
<tr>
<td align="left">x != y</td>
<td align="left">不相等</td>
<td align="left">如果 x 不等于 y，则返回 true</td>
</tr>
<tr>
<td align="left">x &lt;&gt; y</td>
<td align="left">不相等</td>
<td align="left">如果 x 不等于 y，则返回 true</td>
</tr>
<tr>
<td align="left">x !== y</td>
<td align="left">不恒等</td>
<td align="left">如果 x 不等于 y，则返回 true</td>
</tr>
</tbody></table>
<h2 id="三元运算符"><a href="#三元运算符" class="headerlink" title="三元运算符"></a>三元运算符</h2><pre class=" language-php"><code class="language-php"><span class="token punctuation">(</span>expr1<span class="token punctuation">)</span> <span class="token operator">?</span> <span class="token punctuation">(</span>expr2<span class="token punctuation">)</span> <span class="token punctuation">:</span> <span class="token punctuation">(</span>expr3<span class="token punctuation">)</span> </code></pre>
<h2 id="组合比较符"><a href="#组合比较符" class="headerlink" title="组合比较符"></a>组合比较符</h2><p>语法格式如下：</p>
<pre><code>$c = $a &lt;=&gt; $b;</code></pre><p>解析如下：</p>
<ul>
<li>如果 <strong>$a &gt; $b</strong>, 则 <strong>$c</strong> 的值为 <strong>1</strong>。</li>
<li>如果 <strong>$a == $b</strong>, 则 <strong>$c</strong> 的值为 <strong>0</strong>。</li>
<li>如果 <strong>$a &lt; $b</strong>, 则 <strong>$c</strong> 的值为 <strong>-1</strong>。</li>
</ul>
<h2 id="括号的引用"><a href="#括号的引用" class="headerlink" title="括号的引用"></a>括号的引用</h2><p>我们通过括号的配对来明确标明运算顺序，而非靠运算符优先级和结合性来决定，通常能够增加代码的可读性</p>
<h1 id="PHP-If…Else-语句"><a href="#PHP-If…Else-语句" class="headerlink" title="PHP If…Else 语句"></a>PHP If…Else 语句</h1><p>条件语句用于根据不同条件执行不同动作。</p>
<h2 id="PHP-条件语句"><a href="#PHP-条件语句" class="headerlink" title="PHP 条件语句"></a>PHP 条件语句</h2><p>当您编写代码时，您常常需要为不同的判断执行不同的动作。您可以在代码中使用条件语句来完成此任务。</p>
<p>在 PHP 中，提供了下列条件语句：</p>
<ul>
<li><strong>if 语句</strong> - 在条件成立时执行代码</li>
<li><strong>if…else 语句</strong> - 在条件成立时执行一块代码，条件不成立时执行另一块代码</li>
<li><strong>if…elseif….else 语句</strong> - 在若干条件之一成立时执行一个代码块</li>
<li><strong>switch 语句</strong> - 在若干条件之一成立时执行一个代码块</li>
</ul>
<h1 id="PHP-Switch语句"><a href="#PHP-Switch语句" class="headerlink" title="PHP Switch语句"></a>PHP Switch语句</h1><h1 id="PHP-array"><a href="#PHP-array" class="headerlink" title="PHP array"></a>PHP array</h1><h2 id="在-PHP-中创建数组"><a href="#在-PHP-中创建数组" class="headerlink" title="在 PHP 中创建数组"></a>在 PHP 中创建数组</h2><p>在 PHP 中，array() 函数用于创建数组：</p>
<p>array();</p>
<p>在 PHP 中，有三种类型的数组：</p>
<ul>
<li><strong>数值数组</strong> - 带有数字 ID 键的数组</li>
<li><strong>关联数组</strong> - 带有指定的键的数组，每个键关联一个值</li>
<li><strong>多维数组</strong> - 包含一个或多个数组的数组</li>
</ul>
<h2 id="PHP-数值数组"><a href="#PHP-数值数组" class="headerlink" title="PHP 数值数组"></a>PHP 数值数组</h2><p>这里有两种创建数值数组的方法：</p>
<p>自动分配 ID 键（ID 键总是从 0 开始）：</p>
<pre class=" language-php"><code class="language-php"><span class="token variable">$cars</span><span class="token operator">=</span><span class="token keyword">array</span><span class="token punctuation">(</span><span class="token string">"Volvo"</span><span class="token punctuation">,</span><span class="token string">"BMW"</span><span class="token punctuation">,</span><span class="token string">"Toyota"</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
<p>人工分配id键</p>
<pre class=" language-php"><code class="language-php"><span class="token variable">$cars</span><span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">=</span><span class="token string">"Volvo"</span><span class="token punctuation">;</span>
<span class="token variable">$cars</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token operator">=</span><span class="token string">"BMW"</span><span class="token punctuation">;</span>
<span class="token variable">$cars</span><span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token operator">=</span><span class="token string">"Toyota"</span><span class="token punctuation">;</span></code></pre>
<pre class=" language-php"><code class="language-php"><span class="token delimiter">&lt;?php</span>
<span class="token variable">$cars</span><span class="token operator">=</span><span class="token keyword">array</span><span class="token punctuation">(</span><span class="token string">"Volvo"</span><span class="token punctuation">,</span><span class="token string">"BMW"</span><span class="token punctuation">,</span><span class="token string">"Toyota"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">echo</span> <span class="token string">"I like "</span> <span class="token punctuation">.</span> <span class="token variable">$cars</span><span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token punctuation">.</span> <span class="token string">", "</span> <span class="token punctuation">.</span> <span class="token variable">$cars</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token punctuation">.</span> <span class="token string">" and "</span> <span class="token punctuation">.</span> <span class="token variable">$cars</span><span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span> <span class="token punctuation">.</span> <span class="token string">"."</span><span class="token punctuation">;</span>
<span class="token delimiter">?></span>            <span class="token shell-comment comment"># I like volvo,BMW and Toyota.</span></code></pre>
<h2 id="获取数组的长度-count-函数"><a href="#获取数组的长度-count-函数" class="headerlink" title="获取数组的长度 - count() 函数"></a>获取数组的长度 - count() 函数</h2><h2 id="遍历数值数组"><a href="#遍历数值数组" class="headerlink" title="遍历数值数组"></a>遍历数值数组</h2><p>类似c中的for，不同于python中的遍历</p>
<h2 id="PHP-关联数组"><a href="#PHP-关联数组" class="headerlink" title="PHP 关联数组"></a>PHP 关联数组</h2><p>关联数组是使用您分配给数组的指定的键的数组。</p>
<pre class=" language-php"><code class="language-php"><span class="token variable">$age</span><span class="token operator">=</span><span class="token keyword">array</span><span class="token punctuation">(</span><span class="token string">"Peter"</span><span class="token operator">=</span><span class="token operator">></span><span class="token string">"35"</span><span class="token punctuation">,</span><span class="token string">"Ben"</span><span class="token operator">=</span><span class="token operator">></span><span class="token string">"37"</span><span class="token punctuation">,</span><span class="token string">"Joe"</span><span class="token operator">=</span><span class="token operator">></span><span class="token string">"43"</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre>
<pre class=" language-php"><code class="language-php"><span class="token variable">$age</span><span class="token punctuation">[</span><span class="token string">'Peter'</span><span class="token punctuation">]</span><span class="token operator">=</span><span class="token string">"35"</span><span class="token punctuation">;</span>
<span class="token variable">$age</span><span class="token punctuation">[</span><span class="token string">'Ben'</span><span class="token punctuation">]</span><span class="token operator">=</span><span class="token string">"37"</span><span class="token punctuation">;</span>
<span class="token variable">$age</span><span class="token punctuation">[</span><span class="token string">'Joe'</span><span class="token punctuation">]</span><span class="token operator">=</span><span class="token string">"43"</span><span class="token punctuation">;</span></code></pre>
<h2 id="遍历关联数组"><a href="#遍历关联数组" class="headerlink" title="遍历关联数组"></a>遍历关联数组</h2><p>遍历并打印关联数组中的所有值，使用 foreach 循环</p>
<pre class=" language-php+HTML"><code class="language-php+HTML"><?php
$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");

foreach($age as $x=>$x_value)    遍历
{
    echo "Key=" . $x . ", Value=" . $x_value;
    echo "<br>";       #换行
}
?></code></pre>
<hr>
<p>类似python中的字典?</p>
<p>以键值对的形式</p>

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